Non-Invasive Prenatal Testing or NIPT is a blood test that can screen for chromosomal abnormalities during pregnancy. Several different forms of NIPT are available, such as the Harmony test and Panorama test, all of which work in the same way. How are we able to check for genetic problems affecting your baby by taking a sample of your blood?
Collecting the Sample
NIPT such as the Harmony test is performed in the same way as any other blood test
. By the time you are able to have the Harmony test at 10 weeks, you may already have had a blood test as part of your antenatal care. We will collect the sample for NIPT in the same way. A needle will be carefully inserted into a blood vessel, usually in the crook of your elbow. We will fill two small tubes with blood. The samples will then be sent to the lab for testing.
Extracting the DNA
It’s easy to understand how blood tests can help when we want to find out your blood type or check for problems such as anaemia during pregnancy, but how can we use your blood to screen your baby for chromosomal abnormalities? The answer reveals some interesting facts about what is going on in your body during pregnancy.
- Conception happens when an egg and sperm come together to create a single cell carrying DNA from both the father and mother.
- The fertilised egg will form all of the cells of your baby, but it will also create the surrounding structures, including parts of the placenta. All of the cells in the embryo and the placenta come from the same fertilised egg, so they are genetically identical.
- During pregnancy, cells from the placenta or the embryo itself can sometimes break free and enter your bloodstream. Sometimes these cells settle and can live in your body for years. However, it is more common for the cells to break up and release fragments of their contents, including the DNA, which will gradually be broken down in your body.
- There is enough of this cell free DNA from the placenta in your bloodstream during pregnancy that we can collect it and analyse it for chromosomal abnormalities. We can tell which chromosome each fragment came from, so we can tell if your baby is carrying an extra copy of a particular chromosome because there will be more fragments that match it.
Pregnancy is an amazing process and we are still discovering even more incredible ways in which it can affect your body. The fact that we can collect fragments of placental DNA from your blood stream in order to perform the Harmony test and other types of NIPT is just one of the latest advances in antenatal care. We can learn so much about what is going on in your body using ultrasound and tests like NIPT.